Integrated circuits (ICs) fabricated using complementary metal oxide semiconductor (CMOS) technologies are susceptible to alpha particles. Alpha particles may cause single event upsets or soft errors during operation of the IC. In particular, alpha particles can cause ionizing radiation when passing through semiconductor device junctions. The ionizing radiation can upset or flip the state of various semiconductor structures, such as a memory cell (e.g., static random access memory (SRAM) cell, such as a conventional 6-transistor or 6T-SRAM). A common source of alpha particles is the bump material used in assembling, packaging, and/or mounting ICs. For example, the Controlled-Collapse Chip Connection (C4) packaging technology utilizes solder bumps deposited on solder wettable metal terminals of the IC and a matching footprint of solder wettable terminals on a substrate. The solder typically includes approximately 95% to 97% by weight of lead (Pb), with the remainder being made up by tin (Sn), although other materials and percentages of materials can be employed. In general, the most common material used for bumps is lead or a lead alloy. As is well known in the art, lead is a source of alpha particles. Alpha particles from solder bumps can penetrate through the interconnect layer of an IC and reach the underlying semiconductor structures, potentially causing the aforementioned single event upsets.
In a typical pad layout of an IC (i.e., the layout of the solder wettable terminals for the solder balls), the underlying metal layers do not follow a specific pattern. Thus, the interconnect of an IC can include large coincident spaces in the metal on several layers. In this manner, vertical channels can exist through the interconnect in which alpha particles can penetrate to underlying semiconductor structures.
Accordingly, there exists a need in the art for a method and apparatus for interconnect layout in an integrated circuit (IC) that overcomes the aforementioned disadvantages.